The present invention relates, in general, to a container crane, and more particularly to a container crane having a system for determining and correcting a relative position of a load-carrying frame to a transport vehicle.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
A container crane of a type involved here is used for loading and unloading container ships and typically includes a trolley that is movable along a boom and has a hoist mechanism with suspended load-carrying frame, comprised of a spreader and a head block, and for moving a container to and from a transport vehicle. Thus, the container is either unloaded from the ship onto the crane-distal transport vehicle or loaded from the crane-distal transport vehicle onto the ship. Crane constructions are known having only a single trolley for direct transfer of a container from the ship to the transport vehicle, and vice versa, or two separate trolleys, each having its own hoist mechanism. One trolley is hereby referred to as primary trolley and assumes the actual loading and unloading of the ship for placing a container from the ship on a placement area to the side of the crane or for transferring a container from the crane-side placement area to the ship. The other trolley is referred to as gantry trolley and transports the container from the placement area to a crane-distal transport vehicle, or removes the container from the transport vehicle for transfer to the placement area, oftentimes also called reception platform. Current crane installations control the one trolley or both trolleys automatically or at least semi-automatically. Proper loading operation depends especially on the position of a trolley or its load-carrying frame, with or without container, relative to a container to be fetched or relative to a transport vehicle. To achieve a swift loading operation, the load-carrying frame must be precisely and quickly positioned in relation to the container to be grabbed, e.g. on a transport vehicle, so that the load-carrying frame can be placed upon the container and grab the container with its grippers, called flippers. Likewise, positioning during the unloading operation should be executed quickly and precisely, i.e. when a container suspended from the load-carrying frame should be positioned in relation to the transport vehicle and placed thereupon. The alignment of the load-carrying frame, with or without container, in relation to the transport vehicle is oftentimes implemented by the crane operator. Especially, in the case of a two-trolley crane, the crane operator sits substantially vertical above the load-carrying frame in the cab of the gantry trolley, while moving with the gantry trolley, and optically monitors the position of the load-carrying frame in relation to the transport vehicle. Possible positional differences are compensated manually and also undertaken by the crane operator. This course of action is not only imprecise and depends primarily on the competence of the crane operator to recognize a positional difference, e.g. an offset, and to execute proper correction through operation of the lifting gear or the running gear, but is also time-consuming, thus adversely affecting the container transshipment.
It would therefore be desirable and advantageous to provide an improved container crane to obviate prior art shortcomings.